The present invention relates to a broadcast signal receiving system; and, more particularly, to an improved apparatus which is capable of selectively receiving either a satellite broadcast signal or a cable television signal.
Broadcasting systems such as satellite broadcasting, cable television (TV) and the like, have been popularized with the rapid development of new media in recent years.
The satellite broadcasting system, using a satellite positioned at several hundred kilometers high above the earth, is capable of transmitting a broadcast signal to much wider area than other broadcasting systems.
Typically, the satellite broadcasting system transmits a broadcast signal of frequency in the range of 11.7-12.2 GHz having a number of channel signals. The satellite broadcast signal transmitted is received by a low noise blockdown converter (LNBC) mounted in a parabolic antenna and the satellite broadcast signal is converted to a radio frequency (RF) signal in the range of 950-2050 MHz to allow following signal process, e.g., tuning a certain channel signal. The converted RF signal is applied to a tuner mounted in a satellite broadcast signal receiver associated with a TV set. The satellite broadcast signal receiver equipped with the tuner having a tuning frequency in the range of 950-2050 MHz is known to tune and to receive a certain channel signal from the converted RF signal. Typically, each of the channel signals contained in the converted RF signal has a 32 MHz bandwidth.
FIG. 1 shows a schematic block diagram of a conventional satellite broadcast signal receiver. The satellite broadcast signal receiver includes two amplifiers 101, 109, a bandpass filter (BPF) 103, a first and a second local oscillators 105 and 115, a first, a second and a third mixers 107, 119 and 121, a surface acoustic wave (SAW) filter 111, an automatic gain controller (AGC) 113, a shifter 117, and a first and a second low pass filters (LPF""s) 123 and 125.
The RF signal converted by a LNBC (not shown) described above is applied to the amplifier 101 and amplified therein to a predetermined level and then is fed to the BPF 103 having a bandpass filtering frequency in the range of 950-2050 MHz. The BPF 103 filters the RF signal with the bandpass filtering frequency in order to eliminate noises contained in the RF signal, and an output of the BPF 103 is fed to the first mixer 107. Meanwhile, the first local oscillator 105 having a variable oscillation frequency in the range of 1429-2530 MHz generates a certain oscillation signal for tuning a desired channel signal controlled by an oscillation control signal from a controller (not shown), e.g., microprocessor incorporated in the receiver, and provides same to the first mixer 107. The first mixer 107 mixes the output signal from the BPF 103 with the oscillation signal from the first local oscillator 105 to generate a first intermediate frequency (IF) signal of about 479.5 MHz. Subsequently, the SAW filter 111 receives the output signal from the first mixer 107 through the amplifier 109 and generates a waveformed channel signal having about 32 MHz bandwidth. The AGC 113 automatically controls a gain of the channel signal from the SAW filter 111 based on a gain control signal from a following processor (not shown), e.g., video amplifier, for providing a fixed level of video signal at a output of video detector (not shown), and outputs the gain controlled channel signal to the second and the third mixers 119 and 121.
In the meantime, the second local oscillator 115 generates a fixed oscillation signal of, e.g., 479.5 MHz, to the second mixer 119 and the shifter 117. The second mixer 119 mixes the output signal from the AGC 113 with the fixed oscillation signal from the second local oscillator 115 to detect a second IF signal of, e.g. 0 MHz, and provides the second IF signal to the first LPF 123. The shifter 117 shifts the phase of the fixed oscillation signal by 90xc2x0 and outputs the shifted oscillation signal to the third mixer 121. The third mixer 121 mixes the output signal from the AGC 113 with the phase-shifted oscillation signal from the shifter 117 to detect a phase-shifted IF signal of 0 MHz and provides same to the second LPF 125.
Finally, the first LPF 123 filters the output signal of the second mixer 119 with a predetermined cut-off frequency to thereby produce a 16 MHz baseband I signal and the second LPF 125 filters the output signal of the third mixer 121 with the predetermined cut-off frequency to thereby produce a 16 MHz baseband Q signal. The baseband I and Q signals may be used to demodulate them for visual display in a following processor (not shown).
On the other hand, as well known in the art, the cable TV broadcasting system transmits a cable TV signal of, e.g., 54-860 MHz bandwidth through a coaxial cable to a cable TV signal receiver associated with a TV set. The cable TV signal also consists of a number of channel signals, each of them having 6 MHz bandwidth. Moreover, the cable TV signal receiver includes a BPF, a mixer, a local oscillator, a SAW filter, and the like, which are similar to the components of the satellite broadcast signal receiver.
However, to receive the satellite broadcast signal and the cable TV signal, as described above, both the satellite broadcast signal receiver and cable TV receiver are used in spite of the similarity in a structure thereof, thereby resulting in a complexity in the structure and a cost-consuming.
It is, therefore, a primary object of the present invention to provide a method and apparatus for selectively receiving either a satellite signal or a cable TV signal.
In accordance with one aspect of the present invention, there is provided a method for selectively receiving a satellite broadcast signal or a cable television (TV) signal, the method comprising the steps of:
(a) generating a first oscillation signal of a first predetermined oscillation frequency in response to a first oscillation control signal which is issued by a controller when a channel to be tuned to is selected by a user;
(b) receiving the first oscillation signal and either one of the satellite broadcast signal and the cable TV signal and mixing the first oscillation signal with either one of the satellite signal and cable TV signal to provide a first mixed signal having a first intermediate frequency (IF) signal;
(c) filtering the first mixed signal with a first predetermined filtering frequency to produce a waveformed band signal;
(d) selectively generating a second oscillation signal of a second predetermined oscillation frequency or a third oscillation signal of a third predetermined oscillation frequency in response to a second oscillation control signal which is issued by the controller when a broadcast mode signal representing a type of the broadcast signal to tune to, either the satellite broadcast signal or the cable TV signal, is selected by the user;
(e) receiving the waveformed band signal and either the second or the third oscillation signal and mixing the waveformed band signal with either the second or the third oscillation signal to output either a second mixed signal having a second IF signal or a third mixed signal having a third IF signal;
(f) in response to the broadcast mode signal, selectively filtering the second mixed signal with a second or a third predetermined filtering frequency to obtain a channel signal of the cable TV signal or a baseband I signal of the satellite broadcast signal which corresponds to the selected channel; and
(g) shifting a phase of the third oscillation signal by a predetermined degrees to issue a phase-shifted third oscillation signal and mixing the waveformed band signal with the phase-shifted third oscillation signal to generate a phase-shifted mixed signal having a phase-shifted third IF signal and filtering the phase-shifted mixed signal with the third predetermined filtering frequency to obtain a baseband Q signal of the satellite broadcast signal corresponding to the selected channel.
In accordance with another aspect of the present invention, there is provided an apparatus for selectively receiving a satellite broadcast signal or a cable television (TV) signal, the apparatus comprising:
means for generating a first oscillation signal of a first predetermined oscillation frequency in response to a first oscillation control signal which is issued by a controller when a channel to be tuned to is selected by a user;
means for receiving the first oscillation signal and either one of the satellite broadcast signal and the cable TV signal and mixing the first oscillation signal with either one of the satellite signal and cable TV signal to provide a first mixed signal having a first intermediate frequency (IF) signal;
means for filtering the first mixed signal with a first predetermined filtering frequency to produce a waveformed band signal;
means for selectively generating a second oscillation signal of a second predetermined oscillation frequency or a third oscillation signal of a third predetermined oscillation frequency in response to a second oscillation control signal which is issued by the controller when a broadcast mode signal representing a type of the broadcast signal to tune to, either the satellite broadcast signal or the cable TV signal, is selected by the user;
means for receiving the waveformed band signal and either the second or the third oscillation signal and mixing the waveformed band signal with either the second or the third oscillation signal to generate either a second mixed signal having a second IF signal or a third mixed signal having a third IF signal;
means, in response to the broadcast mode signal, for selectively filtering the second mixed signal with a second or a third predetermined filtering frequency to obtain a channel signal of the cable TV signal or a baseband I signal of the satellite broadcast signal which corresponds to the selected channel; and
means for shifting a phase of the third oscillation signal by a predetermined degrees to issue a phase-shifted third oscillation signal and mixing the waveformed band signal with the phase-shifted third oscillation signal to generate a phase-shifted mixed signal having a phase-shifted third IF signal and filtering the phase-shifted mixed signal with the third predetermined filtering frequency to obtain a baseband Q signal of the satellite broadcast signal corresponding to the selected channel.